net: phy: update port type for MoCA PHYs

MoCA PHYs are using coaxial (BNC-like) connectors, update the
transceiver port type when replying to ethtool.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>